Berberine, the major bioactive compound from Berberis aristata, attenuates virulence of multidrug resistant Chromobacterium violaceum at non-lethal concentrations by targeting bacterial efflux and denitrification machinery

Berberis aristata root extract, and berberine were assessed for their anti-pathogenic activity against multidrug resistant Chromobacterium violaceum. Berberine was found to be more potent than the parent extract with respect to attenuation of the pathogens virulence against the model host Caenorhabditis elegans. It also performed better than six different antibiotics, when compared at same concentration. Berberine was able to modulate multiple traits of the target pathogen, such as, biofilm formation, haemolytic activity, efflux/transport activity, and exopolysaccharide production. Repeated exposure of C. violaceum to berberine did not induce resistance. Whole transcriptome analysis of the berberine-treated C. violaceum revealed differential expression of genes associated with stress response, efflux, denitrification, and metalloproteases. Downregulation of two genes of the denitrification pathway, nirK and norB, was confirmed through RT-PCR too.